Split feed &#34;duo-sol&#34; operation



July 10, 1956 F. L. FAST ET AL SPLIT FEED "DUO-SOL" OPERATION 2 Sheets-Sheet l Filed July 25, 1952 Y Q /V P N A .Swmk w23 INVENToR Z. f'as July 10, 1956 F. L. FAST ET A1.

SPLIT FEED "DUO-SOL" OPERATION 2 Sheets-Sheet 2 Filed July 25, 1952 Qh .um E? NXNN United States Patent O 2,754,247 SPLIT FEED DUo-soL OPERATION Fred L. Fast, Sewell, and Harold Button, Pitman, N. J.,

assignors to Soeony Mobil Oil Company, Inc., a corporation of New York Application Jury 2s, 1952, serial No. 300,364 4 Claims. (ci. 19e-14.2)

The present invention relates to the separation of mixtures of hydrocarbons into fractions which are more paratiinic than the charge stock and into fractions more aromatic than the charge stock in which two substantially immiscible solvents are used and the charge is extracted with one solvent in an operation in which at least some part of the extraction with the one solvent takes place in the presence of the other solvent. Such an operation is known as the Duo-Sol process. The present invention relates to an improved method of operating a Duo-Sol unit to obtain an increased yield of ratinate without increasing substantially the total amount of solvents and without changing substantially the ratio of one solvent to the other.

The Duo-Sol process has been described in various publications notably U. S. Patent No. 1,912,348 (May 30, 1933) and Reissue No. 19,763 41,912,349; May 30, 1933) granted to Malcolm H. Tuttle and in Petroleum Refiner, vol. 26, No. 4 Process Handbook Section, page 138. As described in the latter publication: The basic principle of the Duo-Sol process is the simultaneous use of two practically immiscible solvents in an extractor system having one or more extract stripping stages in addition to the conventional rafinate stripping stages. Propane is employed as a parainic solvent and Selecto a blend of phenol and cresol, is the selective naphthenic solvent, separation of the two layers in each extraction stage is accomplished by gravity.

The Selecto layer takes into solution the asphaltic unstable and otherwise undesirable fractions of the charge stock. The propane layer carries the stable paranic lubricating fractions. The two solvents iiow countercurrently through the extractor system, the charge stock being introduced at an intermediate stage. As is shown in the owsheet, the extract layer is contacted with an increasingly concentrated propane solution in owing from stage 3 to stage 1, and is thereby stripped of any paranic fractions it might contain. In a similar manner, as the propane-rainate layer ows in the opposite direction from stage 3 to stage 7, it comes into contact with a more and more concentrated solution of Selecto, thus being stripped of its asphaltic oil content.

Solvent recovery from each layer is accomplished by vaporization of propane in a high pressure tower and the stripping of Selecto from each layer in a low pressure tower.

While a detailed owsheet is provided on page 139 of the aforesaid publication for use in conjunction with the description provided therein, a less detailed and more diagrammatic flowsheet will suice those skilled in the art for an understanding of the present invention. Such a simplified iowsheet is given in Figure HI of the drawings.

As pointed out in the Tuttle patents, a characteristic of a lubricating oil which distinguishes the Pennsylvania lubricating oils from the mixed base Mid-Continent and/or the naphthenic or asphaltic base lubricating oils from the Gulf Coast and California is a difference in the 2,754,242? Patented July 10, 1956 viscosity-gravity constant. Consequently, it has become common practice to use the viscosity-gravity constant (V. G. C.) as a means of determining the quality of a lubricating oil and as a control means in plant operation.

With the increased demands for high grade lubricants, and the decrease in available materials of construction coupled with rising costs of construction, it has been necessary to find some means of increasing the capacity of units such as Duo-Sol units without additions to existing plant facilitiesV which according to widespread opinion among theoreticians and practical men were operating at full capacity. It was surprising therefore to discover that a Duo-Sol plant which was handling its full capacity of charge stock was capable of handling up to and even 100% more of a suitably prepared secondary feed in addition to the full complement of regular primary feed without increasing substantially the total amount of solvent and without changing substantially the ratio of one solvent to the other.

Accordingly, it is an object of the present invention to provide a method of operating a Duo-Sol unit to increase the yield of raffinate of required quality without changing substantially the basic solvent ratios, the total amount of solvents used for extraction per unit time, and without enlarging the extraction unit. It is another object of the present invention to modify the operation of a Duo-Sol extraction unit operating on a charge of feed comprising a long residuum and producing a lubricating oil fraction having a required viscosity-gravity constant (V. G. C.) to increase the yield of lubricating oil fraction without substantial change of total solvent used and the ratio of one solvent to the other by simultaneously treating in addition to said long residuum an amount of at least partially deasphalted oil equivalent to up to of the long residuum. -t is a further object of the present invention to treat substantially simultaneously a long residuum in amount equivalent to the full rated capacity of a Duo-Sol unit and a fraction of mineral oil of the same or different crude, said fraction adjoining said long residuum in end point of boil- 'ing range which has been deasphalted to at least some extent either by distillation or solvent deasphalting, in amount up to 100% of said long residuum without enlarging the extraction capacity of the extraction section of said Duo-Sol unit to obtain a lubricating fraction of required viscosity-gravity constant. Other objects and advantages will become apparent to those skilled in the art from the following discussion taken in conjunction with the drawings in which: Figure I is illustrative of the relation, distillation-wise, of the several fractions of crude oil; Figure Il is illustrative of the relation of primary feed to secondary feed; Figure IH is a owsheet in a more or less diagrammatic manner of the extraction section of a Duo-Sol unit.

Brcadly speaking, the present invention provides a method of increasing the output of rafiinate of required quality from a two solvent extraction system having an extract end and a rainate end in which the solvent for paranic hydrocarbons is introduced near the extract end, the solvent for non-paraiinic hydrocarbons is introduced near the rainate end, and the primary feed is introduced at a point intermediate the center of the system and the extract end by introducing a secondary feed into the system at a point intermediate the ranate end and the point at which the primary feed is introduced into the system. Preferably the primary feed is introduced into the system at a point about midway of the extract end and the midpoint of the system, while the secondary feed is introduced at the midpoint of the system.

Turning to Figure l, the relation of the various fractions into which crude petroleum is divided in the initial stages of refining become apparent. A crude Which has been subjected tofdistillation to a temperature of about 600 F'. is a topped crude and represents a mixture of those components of the original crude boiling above the gas oil range. From the topped crude can be removed the lower boiling lubricating fractions known as the distillates and bright stock. The mixture of components of the crude boiling above the end point of the wax distillates are known as long residuum. By subjecting the long residuum to distillation under vacuum, a lubricating fraction can be recovered which subjected to further refining yields lubricating oil.

When desired, the long residuum, or long resid, can be solvent deasphalted and rened or the long resid can be subjected to the reiining action of the Duo-Sol process without deasphalting by either distillation or solvent deasphalting. Furthermore, a long resid can be partially deasphalted by solvent deasphalting and a partially deasphalted oil having a Conradson Carbon Residue of about 4 to about 6 weight per cent obtained and this` in turn further rened by the Duo-Sol process.

The present improved method of operating a Duo-Sol unit provides for treating an undeasphalted long resid and a fraction adjoining it simultaneously in a Duo-Sol unit the total volume of the two feed stocks being substantially greater, up to 100%, then the rated capacity of the Duo- Sol unit for the long resid.

By fraction adjacent is meant, a fraction of topped `crude having an end point approximating or somewhat higher than the initial boiling point of a short residuum, or short resid. Thus, such a fraction is quite similar to a long resid or a short resid in that a major portion if not all of the constituents thereof are of the same molecular weight and chemical constitution as the non-asphaltic portion of a long or short resid.

Thus, considering Figure Il a long resid contains paraffinic hydrocarbons P, non-parafinic hydrocarbons N, and asphaltic materials A. In the Duo-Sol process the paraffinic hydrocarbons are removed as a propane solution known as the raffinate while the non-parafiinic hydrocarbons N and asphaltic materials A are removed as a Selecto solution thereof known as the extract. The long resid containing paraiiinic hydrocarbons, nonparanic hydrocarbons and asphaltic material is a primary feed to a Duo-Sol unit.

The secondary feed can be either an adjoining fraction 1, having an end boiling point substantially the same or somewhat higher than the initial boiling point of a short resid, a partially deasphalted long resid 2, an adjoining fraction 3 or a partially deasphalted fraction 4. It will be noted that all of these secondary feeds have a characteristic common to each of them and to the primary feed, i. e., they all contain constituents of substantially the same molecular weight and have a distribution of paraiiinic and non-paraf'rinic hydrocarbons similar to that of the primary feed.

The use as secondary feeds of fractions such as adjoining fraction 1, adjoining fraction 3, partially deasphalted fraction 4 and deasphalted long resid is not to be confused with the use as a secondary feed of a fraction containing little if any constituents having a molecular weight corresponding to that of the preponderant portion of the hydrocarbons in a long resid, i. e., the hydrocarbons as distinct from the asphaltic materials.

Thus, for example, a wax distillate boiling below Y 500 F. at l0 mm. Hg was dewaxed and the dewaxed oil redistilled under a vacuum to give an overhead cracklng stock and a bottoms. The physical characteristics of Y both a dewaxed neutral and a bright stock obtained by redistillation of a small portion of a Duo-Sol Split Feed rainate, produced from a commercial Duo-Sol operatron employing two parts by volume of a residuum nl. and one part by volume of a distillate having a viscosity of 43 S. U. S. Vat 210 F., are presented below:

Redistillation of Duo-Sol Ra'inate Duo-Sol Rafnate Y Neutral Bright Over- Stock head Bottoms Yield, Percent Volume 100.0 10.0 90. O Gravit, I. l i 30.0 25,4 F 25 35 30 Flash, F., C O 400 540 S. S. U. 157 1,866 S. S. U. 210 F 43. 6 123 Viscosity Index 97 93 Lovibond C or. 1.0 A. S. T. M. Color 1- 8- Carbon Residue, Percent Wt 0.01 0. 33 Sulphur, Percent Wt 0.31 0. 70

The viscosity index data show that when Duo-So reining such a mixture of distillate bottoms and resid there is a tendency to over-refine the distillate bottoms and under-refine the resid.

The data presented in Tables I .and II show that similar quality products, based on viscosity index, can be prepared by either blending a Duo-Sol refined bright stock and a conventionally acid-refined neutral or by Duo- Sol rening the same materials by the split-feed technique wherein the charge to the Duo-Sol was composed of two parts by volurnn of residuum and one part by volume of a distillate having a viscosity of 43 S. U. S. at 210 F.

TABLE I Typical physical characteristics of Duo-Sol split-feed rafjnate Duo-Sol Split-Feed Rafnate Dewaxed Waxy Dewased Blend Blend Blend Percolated V.G.C

TABLE ll Dewaxed Blend Percolated 44:1

Dewaxed Blend Waxy Blend The data presented in Table Ill further establishes the fact that in the split-feed operation of a Duo-Sol unit of commercial size the effect upon the raffinate produced, based on viscosity index, is comparable to that obtained when blending a Duo-Sol treated bright stock and a conventionally rened neutral. The data below are typical of Duo-Solfoperations when employing the split-feed technique and using a distillate yhaving a viscosity of 44.6 S. U, S. 210 F. for the secondary charge stock.

TABLE III Treated Oil Tar Average No. 50 gal. bbls. Av Av. Av. Charged] Grav Av. Av. Av. yield Percent bbls. Percent day Grav. Vis. V. G. C. bbls. yield per yield @210 per day day gelsid 6} 8. g5 29. 1 85. 6 0. 7999 1, 631 54. 6 l, 354 45. 4

p'tee: esi 3 1. Distillate 910 "z l 153 26. 4 28. 4 6a. 0 0. 8111 2, 576 75. 1 852 24. 9

Assuming the primary feed, resid 361/2, in the split-feed operation were refined to the same extent as when refined as the sole feed, then from 2211 barrels about 1000 barrels of tar would be recovered. However, only 852 barrels of tar were obtained.

It was previously established that the use of a distillate with a nal boiling point in the order of 500 F. 10 mm. of Hg resulted in a tendency to over-refine the neutral and under-refine the residual fraction. In addition, on the basis of the following data and computations it is manifest that the split-feed operation, as in Table III, makes it possible to obtain additional retned oil from the primary residuum charged to the unit. This incremental oil which is of lower viscosity index (see Table III) may be used because of the increase in viscosity index due to blending the neutral and bright stock within the Duo- Sol extraction system. When the 361/2 stock was refined alone the treated oil had a viscosity of 85.6 seconds at 210 F. When the 361/2 stock and 910 stock were refined in the split-feed operation, the treated oil had a viscosity of 65.0 seconds 210 F. Whereas, had the same quantity of 910 stock (see Table III) been Duo-Sol relined alone in the normal manner, about 960 barrels of the same viscosity index ranate with a viscosity of 44 seconds 210 F. would be produced. Duo-So refining of the 2211 barrels of 361/2 stock in the normal manner would have resulted in production of about 1210 barrels of the same viscosity index (98) bright stock as indicated in Table III having a viscosity of 85 .6 seconds at 210 F. Thus, from Duo-Sol refining the neutral and residuum individually in blocked operations, 2130 barrels of oil would have been produced having a blended viscosity index of about 100 and a viscosity, based on blending charts, of 60 at 210 F. However, in the split-feed operation 2576 barrels of a 65.0 S. U. V. 210 F., 98 viscosity index oil, were obtained. It is thus manifest that 446 barrels of additional oil were obtained by utilizing split-feed Duo-Sol operations. From blending charts this recorded oil has a viscosity of 105 at 210 F. and a calculated viscosity index of about 92. Thus, it is established that a stock in which the major constituents have a molecular Weight of a diierent order compared to the molecular weight of the major portion of the paraiiinic constituents of a resid, results in sub-standard refining of the rainate obtained from the resid, but increases the yield and viscosity of the raffinate therefrom. Consequently, to obtain the same severity of relining on the resid fraction when split-feeding a 910 stock or similar neutral stocks as obtained when Duo-Sol reiining the resid alone, increased reining severity, attended by a probable sacrice in resid raffinate productions, would be required. However, when a fraction having a major portion of its constituents of the same order of molecular weight and comparable or increased paranicity as the preponderant portion of the parainic constituents of the primary feed is used as a secondary feed in split-feed operation of a Duo-Sol unit, the primary eiect is a refining of the secondary feed to the same level as the primary feed without a decrease in the capacity of the Duo-Sol unit to rene the primary feed. This is demonstrated by a comparison of data obtained in the customary operation of a Duo-Sol unit in which the sole feed is a resid (PT 361/2) with data obtained in split- TABLE IV Feed: Feed: Resid 'IP 361/2 Barrels per day 4,330 Pounds per hour 103 63.5 Rainate:

Barrels per day 2,215 Volume per cent yield 51.1 A. P. I. gravity 26.8 Viscosity 210 F 120 V. G. C 0.8090 V. L 91 Tar:

Barrels per day 2,115 Volume per cent yield 48.9 CaHa, pounds per hour 103 155 Selecto, pounds per hour 103 143 selecto-propane 0.92

Propane Selecto mea-2.44 Charge-225 TABLE V Feed: Feed: Resid TP 361/2 Barrels per day (resid TP 361/2, 4191,

88.7%) (Hy 16, 534, 11.3%) 4,725 Pounds per hour 103 71.8 Rainate:

Barrels per day 2,700 Volume per cent yield 57.1 A. P. I. gravity 27.4 Viscosity 210 F 97.8 V. G. C 0.8100 V. I 94 i Tar:

Barrels per day 2,025 Volume per cent yield 42.9, CaHa, pounds per hour 103 155 Selecto, pounds per hour 103 143 selecto-propane 0.92

Propane 155 2 43 TP 36% Charge-.887018) X 10V-63.7- selecto 143 TP 36% Chrge`f3.` 2'23 Hy 16 10 mm 760 mm.

32o 56o 472 500 556 son 606 625 875 feed operation are given in Table V. v

data for split-v i Those skilled in the art will recognize that both' raffinates are of equal quality as determined by V. G. C. and V. I. Those skilled in the artwill also note that the yield of raffinate from the split-feed operation exceed that from the usual mode of operation by about 6% on a yield of 2215 barrels of railinate per day. VWhen this increase in yield of rainate is obtained for a years operation of say 300 days at a throughput of say about 4000 barrels per day, the' increased yield is about 44,500 barrels of rainate per year. Furthermore, it will be noted that such an increase is based upon the use of secondary feed to the extent of only about l volume per cent of the primary feed whereas the presentV invention includes the use of secondary feed to equal up to 90% of the primary feed.

Similarly, a residuum designated as PHP-356, was treated in the usual manner as the sole feed to a Duo- So unit and subsequently was treated as a primary feed with an overhead'cylinder stock, designated Hyl6, as a secondary feed. The data obtained in these comparative runs are presented in Table VII.

run between a residuum, designated Hy-361/2 as a sole feed and one in which the same resid (Hy-361/2) was the primary feed and the overhead cylinder stock IIy16 was the secondary feed was made. The data for this comparison are given in Table VIII.

TABLE VII f-- PHF356 PHF-356 Hy-l Feed:

Barrels per day 2, 955 2, 953 458 Pounds per hour 103 38. 4 39. 2 6.1

Ranate:

Barrels per day l, 857 2, 382 Volume percent yield 63. 5 68. 6 Tar:

' Barrels per day 1, 068 1, 089 Volume percent yield... 36. 5 31. 4 Propane Feed 4.00 l 4. 09 Seleoto Feed 3. 60 l 3. 85 Salento/Propane 0. 90 0. 94

'1 Based upon the PEF-356 charged.

TABLE VIII HYT-Bl/ EXT-36% Bly-16 Feed:

Barrels per day 2. 932 2, 718 572 Pounds per hour 103 41. 6 41.1

Ranate:

Barrels per day l, 443 1, 959 Volume percent yield 49. 1 55. 0 Tar:

Barrels per day 1, 496 1, 602 Volume percent yield.. 50. 9 45. 0 Propane Feed 3. 95 1 3. 99 Selecto Feed 3. 13 1 3. 08 Selecto/Fropaue 0. 79 0. 77

. 1 Based upon the HYT,? 6% charged.

' Ranates from PEF-356 FHF-356 EXT-36% HYT-36% f )Ely-16 Hy-l A1 P. I. Gravity- 27.9 28.0 27.4 27.7 Viscosity seo. 210

F 124. 3 119. 0 114 97.8 V. G. O 0. 8017 0. 8019 0.8057 V0. 8077 Another comparative It'is manifest that, although the oil to solvent Yratio based upon the amount of residuum charged in splitV was the same as that based upon'total feed operation charge in normal operation, more charge as a secondary about 10 volume per cent feed was treated with an increase yield of rainate of substantially the same qualityY per cent yield and had the following characteristics:

Gravity, A. P. I. 27.2 Viscosity, sec., S. U. V. 210 F 76.3 0 8155 V. G. C.

Specific gravity 0.9357 I. B. P. F 149() 5% F 784 10% F-- 922 20% F 947A 30% F 960 40% 2 975 1 Corrected to '760 mm. 1 Began to crack.

were made with the same solvent ratios based upon the amount of residuum charged (by weight).

of the primary feed. The

The secondary feed was a solvent` avete/i7* TABLE IX Secondary feed-solvent deasphalted Raw Deas- Test No Resid pgzlt 1 Resid, Percent wt. ot' charge Deasphalted Oil, wt. per cent of charge Av. Sp. Gr. 60 F 1 Based upon resid charged. 2 Dewaxed ranate. 3 Based upon resid capacity yield.

A brief study of the data presented in Table IX `establishes that the dewaxed raiinate produced in tests 3, 4 and 5 is 'the equivalent in quality of the dewaxed raffinate produced in test No. 1 in which -the unit Was operated at full capacity with the resid as the sole charge. It will be noted that increasing the secondary feed to as much as 50% of the primary feed did not adversely affect the quality -of Ithe raffinate and that, while the quality of the ranate can be raised slightly by increasing the relative amount lof Selecto used, the slight increase in quality is overbalanced by Ithe decrease in yield (tests 4 and 5) It is interesting to note that as the amount of deasphalted oil-secondary feed is increased a greater portion of the expected increase `of rainate is obtained. Thus, the secondary feed when treated in the Duo-Sol feed as the sole unit yielded 65.7 volume per cent raiinate. When an amount of secondary feed equivalent to by Weight of 'the primary feed is charged to the unit, fthe relative total product is calculated -to be 186%. Actual tests produced a relative total production of 164%. When -the secondary feed represents (by Weight) of Ithe primary feed, the calculated relative total production is 266%. The yield actually obtained lis 256%. Thus, it is apparent that as the amount of secondary feed charged approached 100% (by Weight) of the primary feed the eciency of -treating approached 100% of theoretical for deasphalted oils of, say, up `to about 2.5 wt. percent Conradson Carbon Residue.

In further demonstration of the advantages accruing from the use of a secondary feed in addition to a primary feed of a. Duo-Sol unit operating at rated full capacity are the data presented in Table XI. In 4the operati-on from which the aforesaid data were obtained a propane deasphalted resid was introduced into compartment No. 5 of a nine .cell Duo-Sol unit as a secondary feed while a crude resid Was introduced into compartment No. 3 of the unit. The naphthenic solvent, Selecto (containing 69% phenol) was introduced into compartment No. 8 While 64% of the propane was introduced into compartment No. 1 and 36% of the propane into compartment No. 4.

A further modification included in the basic concept is illustrated by run No. 2 of Table X wherein a propane deasphalted resid and an -overhead cylinder stock were introduced into compartment No. 5 as secondary feed, crude resid vwas introduced into compartment No. 3 as primary feed and the Selecto and propane introduced into :the unit as in run No. l. The crude resid, the propane deasphalted resid, and .the blend of propane deasphalted resid and overhead cylinder stock yielded the following inspection data:

TABLE X Run No. 1 Run N o. 2

Blend of PD 30 Resid Resid Resid elg head Cyl. Stock Gravity 13. 8 20. 8 8 20. 6 SSU 210 F 1, 366 154 1, 420 118 Overhead cylinder stock Gravity, A. P. I SSU 210 F Flash (0.0.C.),F

Distillation 10 mm. Hg 760 mm. Hg

P. D. Resid 60 Overhead Distil1ate Total 4, 824 4, 835 Yield Rafnate, percent VOL 41. 42. 9 O-S-P Ratio 1 2. 9:2. 1 1:2. 9:2. 2 Selecta/Propane 1. 1. 29 Physical Properties:

Having demonstrated the unobvious results obtained by Duo-Sol unit stre'ated A f is introduced and the `cell into which the solvent for non-Y parafhnic hydrocarbons is lintroduced, the novel split-feed operation will be discussed in sufficient detail in .conjunction with Figure III for those skilled in the art to understand the modus operandi. m .Y

Let us assume that a Duo-Sol unit is being operatedv on a given residuurn at full capacity to produce a rafnate of given quality. being produced under conditions of a given resid-solvent for non-parainic hydrocarbons-solvent for parainic hydrocarbons ratio by weight. (In the following discussion the solvent for non-parainic hydrocarbons will be considered to be Selecto a mixture of about 65% 20% phenol and the balance mixed cresols and the solvent for paraftinic hydrocarbons will be considered to be propane.) Without changing the resid-Selectopropane ratio a secondary feed comprising an at least partially 12 with the propane solution from cell #5 and the extract solution fromv cell #6 and each fraction of the secondary feed is then Ysubjected to contact with leaner and leaner Selecto solution or leaner and leaner propane solution respectively asthe reined oil travels with the refined oilv of the primary feed to cell #9 andV theY Selecto extract of the primary feed travel'rto cell #1. The refined oil The required results are then l0 to about deasphalted fraction of mineral oil sufficiently close to said resid to have a specific gravity of not less than about 90% of that of the resid being treated is introduced into a cell intermediate the cell into which the resid is introduced and the cell into which the Selecto is introduced. The secondary feed is introduced into the unit without an appreciable increase in the amount of Selecto or propane being charged to the unit since the object, brieiiy stated, is to increase the output of raffinate of required quality from the unit without increasing the amount of solvent in circulation. Other operating factors and operating conditions are maintained substantially the same as they were before introduction of the secondary feed.

Assuming that the resid to be treated has not been treated previously in the unit. Generally, previous laboratory tests have established the probable'optimum conditions for treatment. Consequently, there is no dif- Iiculty for those skilled in the operation of a Duo-Sol unit to translate the laboratory results into refinery practice.

While at the present time it is preferred to introduce the primary feed into the #3 cell of the unit and to introduce the secondary feed into the #5 cell ofthe unit, in general the secondary feed can be introduced into any one or all of the cells 4, 5, 6 and 7. cell unit with the primary feed introduced into the #3 cell, the secondary feed can be introduced into either the #4 or the #5 cell, or into both. In other words, it is preferred to introduce the secondary feed into the middle cells ofthe unit.

In the event that the unit is a 7- 45 A conventional Duo-Sol 9 cell umt is represented,

without auxiliary equipment such as pumps, heat exchangers, solvent separating and recovery systems etc., in Figure III. The cells are numbered consecutively beginning with the cell 1 into which the propane is introduced through 575 pipe 11 and from which the extract (Selecto solution or suspension of asphaltic material and other undesirable constituents of the feed) is discharged through pipe 12. Selecto is introduced through line 29 into the last cell (#9 to Fig. III) from which the rainate (propane solu- 50 tion of refined oil) is discharged through pipe 30. The primary feed, i. e., resid is introduced into cell #3 through pipe 13 Where the feed encounters the two solvents, is thoroughly mixed therewith and settled into two phases, a

propane-oil phase and a Selectoasphalt phase by gravity. 55

Mixing and settling occurs in each cell, the propane solution of treated oil owing counter-current to a'leaner and leaner Selecto stream as the refined oil passes'from cell to cell to the discharge cell #9. The propane solution of refined oil passes from cell #1 to cell #9 through 70 pipes 14, 15, 16, 17, 18, i9 and 20 while the Selecto extract passes from cell #9 to cell #1 through pipes 21, 22, 23, 24, 25, 26, 27 and 28. Secondary feed is introduced into one'or more `of the middle cells of the unit such as cell #5 through line 31, contacts and is mixed is then further treated as required such as by percolation drocarbons having a molecular weight of the same order as the non-asphaltic constituents of thc resid. The Vsecondary feed can be completely deasphalted or partially deasphalted. Thus, referring to Fig. I the primary feed can be a long resid having an initial boiling point of at least about 300 F. at l0 mm. of mercury or a short resid having an initial boiling point at least of about 500F. to 550 F. at l0 mm. of mercury. With either resid as a primary feed, a fraction having an initial boiling'point of at least 300 F. and of substantially reduced asphalt content can be used as a secondary feed. The secondary feed can have an asphaltic' content sucient `to yield a Conradson Carbon Residue of about 0.1 to about 2.5 to about 3 wt. per cent. Another means of characterizing a suitable secondary feed is to say that it has a specific gravity at least about of that of the resid to be treated as a primary feed. The fractions 1, 2, 3, 4, 5 and similar fractions diagrammatically indicated in Figure Il, deasphalted or partially deasphalted either by distillation or solvent deasphalting or similar fractions which are obtained from crudes containing little Yor no asphalt can be treated as secondary feeds. However, fractions such as diagrammatically indicated at 6 of Figure II whether from asphaltic base or non-asphaltic baseV crudes cannot be treated and the rening effect obtained thereon.

From the foregoing discussion of the modus operandi of, and the results obtained from, the present novel split-feed operation of a Duo-Sol extraction unit it is manifest that the present invention comprises introducing a primary feed into a compartment of a Duo-Sol unit intermediate the point of introduction o-f the solvent for parafiinic hydrocarbons and the middle compartment of the extraction unit introducing a secondary feed into at least one compartment intermediate the point of introduciton of said primary feed and the cell into which the solvent for non-paraifinic hydrocarbons is introduced and treating the primary and secondary feed with amounts of solvent for paranic hydrocarbons and solvent for nonparanic hydrocarbons in substantially the same proportion and in substantially the same amount as required to treat the amount of primary feed being treated in a unit of time to produce a ranate of the required quality.

We claim:

l. InY the art of refining mineral oil in which an oil comprising parafnic and non-parainic constituents as a primary feed is extracted in a plurality'of stages providing for countercurrent passage therethrough of a sol-` vent and an added liquid adapted to form a two-liquid solvent system with a solvent having greater solvent power for non-paratiinic than for parafinic constituents introduced into the final stagein the presence of an added liquid having greater solvent power for paraftinic than for non-parafrinic constituents introduced into the initial stage and in which an extract phase is withdrawn from'said initial stage anda raffinate phase is withdrawn from the final stage, the improvement which comprises introducing said primary feed into a stage intermediate the initial stage and themid-point of said plurality of stages, selecting a secondary feed, consisting of an at least' partially deasphalted oil, other than said primary feed,r`naving a specific gravity not less than 90 per cent of the specific gravity of said primary feed, having'a preponderant portion of the as that of the non-asphaltic constituents of said primary feed and having a distribution of parafnic and nonparainic hydrocarbons similar to that of the primary feed, Whilst introducing said primary feed at a maximum rate concomitant with maximum yield of a ranate of required quality, introducing said secondary feed into least one stage intermediate the stage into which said primary feed is introduced and the final stage of said plurality of stages, and without increasing substantially the amount of said solvent or said added liquid but with an amount of said solvent and said added liquid sucient to produce phase separation in the stage into which said primary feed is introduced, treating said primary feed and said secondary feed simultaneously to produce an increased yield of rainate of substantially the same quality as produced when treating said primary feed.

2. The improvement of claim 1 wherein the primary feed is selected from the group consisting of long and short residua.

3. The improvement of claim l wherein the primary feed is selected from the group consisting of long and short residua, the primary feed is introduced into the stage midway the initial stage and the mid-point of said plurality of stages, and the secondary feed is introduced into the stage at the mid-point of said plurality of stages.

4. The improvement of claim 1 wherein the primary feed is selected from the group consisting of long and short residua and the secondary feed adjoins the end boiling point of said primary feed.

References Cited in the file of this patent UNITED STATES PATENTS 2,070,385 Tuttle Feb. 9, 1937 2,079,886 Voorhees May 11, 1937 2,225,396 Anderson Dec. 17, 1940 2,687,982 Baumann Aug. 3l, 1954 

1. IN THE ART OF REFINING MINERAL OIL IN WHICH AN OIL COMPRISING PARAFFINIC AND NON-PARAFFINIC CONSTITUENTS AS A PRIMARY FEED IS EXTRACTED IN A PLURALITY OF STAGE PROVIDING FOR COUNTERCURRENT PASSAGE THERETHROUGH OF A SOLVENT AND AN ADDED LIQUID ADAPTED TO FORM A TWO-LIQUID SOLVENT SYSTEM WITH A SOLVENT HAVING GREATER SOLVENT POWER FOR NON-PARAFFINIC THAN FOR PARAFFIN CONSTITUENTS INTRODUCED INTO THE FINAL STAGE IN THE PRESENCE OF AN ADDED LIQUID HAVING GREATER SOLVENT POWER FOR PARAFFINIC THAN FOR NON-PARAFFINIC CONSTITUENTS INTRODUCED INTO THE INITIAL STAGE AND IN WHICH AN EXTRACT PHASE IS WITHDRAWN FROM SAID INITIAL STAGE AND A RAFFINATE PHASE IS WITHDRAWN FROM THE FINAL STAGE, THE IMPROVEMENT WHICH COMPRISES INTRODUCING SAID PRIMARY FEED INTO A STAGE INTERMEDIATE THE INITIAL STAGE AND THE MID-POINT OF SAID PLURALITY OF STAGES, SELECTING A SECONDARY FEED CONSISTING OF AN AT LEAST PARTIALLY DEASPHALTED OIL, OTHER THAN SAID PRIMARY FEED, HAVING A SPECIFIC GRAVITY NOT LESS THAN 90 PER CENT OF THE SPECIFIC GRAVITY OF SAID PRIMARY FEED, HAVING A PREPONDERANT PORTION OF THE HYDROCARBONS THEREOF IN THE SAME MOLECULAR WEIGHT RANGE AS THAT OF THE NON-ASPHALTIC CONSTITUENTS OF SAID PRIMARY FEED AND HAVING A DISTRIBUTION OF PARAFFINIC AND NONPARAFFINIC HYDROCARBONS SIMILAR TO THAT OF THE PRIMARY FEED, WHILST INTRODUCING SAID PRIMARY FEED AT A MAXIMUM RATE CONCOMITANT WITH MAXIMUM YIELD OF A RAFFINATE OF REQUIRED QUALITY, INTRODUCING SAID SECONDARY FEED INTO AT LEAST ONE STAGE INTERMEDIATE THE STAGE INTO WHICH SAID PRIMARY FEED IS INTRODUCED AND THE FINAL STAGE OF SAID PLURALITY OF STAGES, AND WITHOUT INCREASING SUBSTANTIALLY THE AMOUNT OF SAID SOLVENT OR SAID ADDED LIQUID BUT WITH AN AMOUNT OF SAID SOLVENT AND SAID ADDED LIQUID SUFFICIENT TO PRODUCE PHASE SEPARTION IN THE STAGE INTO WHICH SAID PRIMARY FEED IS INTRODUCE, TREATING SAID PRIMARY FEED AND SAID SECONDARY FEED SIMULTANEOUSLY TO PRODUCE AN INCREASED YIELD OF RAFFINATE OF SUBSTANTIALLY THE SAME QUALITY AS PRODUCED WHEN TREATING SAID PRIMARY FEED. 